1. Technical Field
The present invention relates to sensors, and more particularly to a gas sensor having a micro-package structure and a method for making the gas sensor.
2. Description of Related Art
A gas sensor works by using applicable electric signals to convert a certain gas in the air into figures for convenient monitoring and calculation. In the air, most gases are colorless and odorless, and thus undetectable by human olfaction or other human sensory functions. However, some of the gases may be dangerous when presenting in the air we breathe. Carbon monoxide, for example, when inhaled excessively by people, the people can be poisoned to faint or even die. This can be prevented and human safety can be ensured by using a gas sensor and taking appropriate ventilating measures. In another instance where the levels of carbon dioxide and oxygen in the air are to be controlled for people's good life quality, a gas sensor may be attached to an air-conditioning system so that when the level of carbon dioxide is higher than desired, the air-conditioning system can activate its air purifier to improve the air quality. It is thus evidenced that gas sensors are important to improvement in comfort and safety of human life.
FIG. 1 and FIG. 2 depict a conventional solid-electrolyte gas-sensing module 1, which comprises a substrate 2, a gas-sensing element 3 deposited on the substrate 2, and a metal cover 4 fixed to the substrate 2 and covering the gas-sensing element 3. The gas-sensing element 3 is composed of a solid electrolyte 5 of cation (Na+) and a printed heater (RuO2) 8 provided between a cathode (sensing electrode) 6 and an anode (counter electrode) 7. The cathode 6 is made from lithium carbonate and gold, and is connected to a first leading pin S1. The anode 7 is made of gold, and is connected to a second leading pin S2. The printed heater 8 is connected to a third leading pin (not shown) and a fourth leading pin (not shown). The gas-sensing element 3 further uses platinum wires to connect connecting pins 9 made of nickel for signal transmission. Such a gas-sensing module 1 has been rapidly developed for having advantages of high conductivity, high sensitivity, and high versatility as the gas-sensing element 3 can be modified by varying the ions generated in the material through absorption, the moving ions in the electrolyte, and the immobilized ions in the material. However, the gas-sensing element 3 is structurally complex and requires high manufacturing costs, so the price of the entire gas-detecting module 1 is consequently expansive. In addition, since a gas-sensing structure of this type is typically made as a voluminous modularized device, its use is subject to spatial abundance.
To sum up, the conventional gas-detecting module is imperfect and needs to be improved.